Quantum mechanics is one of the best-tested theories in science, and it’s one of the few where physicists get to do experiments proving that Einstein was wrong.

That’s what a team at Griffith University and the University of Tokyo in Japan did this week, showing that a weird phenomenon — in which the measurement of a particle actually affects its location — is real.

Back in the 1920s and 1930s, Albert Einstein said he couldn’t support this idea, which he called “spooky action at a distance,” in which a particle can be in two places at once and it’s not until one measures the state of that particle that it takes a definite position, seemingly with no signal transmitted to it and at a speed faster than light. When the particle takes its definite position, physicists refer to this as its wave function collapsing.

The phenomenon was outside of contemporary experience in physics and seemed to violate the theory of relativity, which posits that the speed of light is an absolute limit on how fast any information can travel. Einstein proposed that the particle isn’t in a superposition state, or two places at once; but rather it always has a “true” location, and people just couldn’t see it. [How Quantum Entanglement Works (Infographic)]

Using a single photon (particle of light), the Australian and Japanese researchers ran an experiment showing that measuring a property of a quantum particle in one place will affect what one sees in another place. That is, they showed that superposition and collapsing wave function are real phenomena.

Alice and Bob

The phenomenon is demonstrated with a thought experiment in which a light beam is split, with one half going to Alice and the other to Bob. Alice then indicates if she detected a photon and if so what state it is in — it might be the phase of the wave packet that describes the photon. Mathematically, though, the photon is in a state of “superposition,” meaning it is in two (or more) places at once. Its wave function, a mathematical formula that describes the particle, seems to show the photon has no definite position.

“Alice’s measurement collapses the superposition,” meaning the photons are in one place or another, but not both, Howard Wiseman, director of Griffith University’s Center for Quantum Dynamics, who led the experiment, told Live Science. If Alice sees a photon, that means the quantum state of the light particle in Bob’s lab collapses to a so-called zero-photon state, meaning no photon. But if she doesn’t see a photon, Bob’s particle collapses to a one-photon state, he said.

“Does this seem reasonable to you? I hope not, because Einstein certainly didn’t think it was reasonable. He thought it was crazy,” he added, referring to the fact that Alice’s measurement looked like it was dictating Bob’s.

The paradox was partially resolved years later, when experiments showed that even though the interaction between two quantum particles happens faster than light (it appears instantaneous), there is no way to use that phenomenon to send information, so there’s no possibility of faster-than-light signals.

Splitting photons

The team at Griffith, though, wanted to go a step further and show that the collapsing wave function — the process of Alice “choosing” a measurement and affecting Bob’s detection — is actually happening. And while other experiments have shown entanglement with two particles, the new study entangles a photon with itself.

To do this they fired a beam of photons at a splitter, so half of the light was transmitted and half was reflected. The transmitted light went to one lab and the reflected light went to the other. (These were “Alice” and “Bob” of the thought experiment.)

The light was transmitted as a single photon at a time, so the photon was split in two. Before the photon was measured, it existed in a superposition state.

One lab (Alice) used a laser as a reference, to measure the phase of the photon. If one thinks of light as a repeating sine wave, phase is the angle one is measuring, from 0 to 180 degrees. When Alice changed the angle of her reference laser, she got varying measurements of the photon: Either her photon was in a certain phase or it wasn’t present at all.

Then the other lab (or Bob) looked at their photons and found the photons were anti-correlated with Alice — if she saw a photon he did not, and vice versa. The state of Bob’s photon depended on what Alice measured. But in classic physics that shouldn’t happen; rather, the two particles should be independent of one another.

Quantum computing

Akira Furusawa, professor of applied physics at the University of Tokyo and one of the co-authors on the study, said the experiment helps explore different kinds of quantum information processing — and with it, communications and computing.

“Usually there are two types of quantum information processing,” he said. “There’s the qubit type, the digital information processing, and there’s continuous variable, a sort of analog type of quantum information. We are trying to combine them.” Conventional processing often relies on counting photons, but this kind of measurement of single photons is more efficient, he said.

Wiseman said one application is in the security of communications.

“Our experiment is a more rigorous test of the properties of such states than has ever been done before, in the sense that we don’t have to trust anything that is happening in Alice’s laboratory. This could be useful for communicating secrets when not all the parties are trusted.”

The experiment is described in the March 24 issue of the journal Nature Communications.

New Time Travel Simulation May Resolve ‘Grandfather Paradox’

On June 28, 2009, the world-famous physicist Stephen Hawking threw a party at the University of Cambridge, complete with balloons, hors d’oeuvres and iced champagne. Everyone was invited but no one showed up. Hawking had expected as much, because he only sent out invitations after his party had concluded. It was, he said, “a welcome reception for future time travelers,” a tongue-in-cheek experiment to reinforce his 1992 conjecture that travel into the past is effectively impossible.

But Hawking may be on the wrong side of history. Recent experiments offer tentative support for time travel’s feasibility—at least from a mathematical perspective. The study cuts to the core of our understanding of the universe, and the resolution of the possibility of time travel, far from being a topic worthy only of science fiction, would have profound implications for fundamental physics as well as for practical applications such as quantum cryptography and computing.

Closed time like curves

The source of time travel speculation lies in the fact that our best physical theories seem to contain no prohibitions on traveling backward through time. The feat should be possible based on Einstein’s theory of general relativity, which describes gravity as the warping of spacetime by energy and matter. An extremely powerful gravitational field, such as that produced by a spinning black hole, could in principle profoundly warp the fabric of existence so that spacetime bends back on itself. This would create a “closed timelike curve,” or CTC, a loop that could be traversed to travel back in time.

Hawking and many other physicists find CTCs abhorrent, because any macroscopic object traveling through one would inevitably create paradoxes where cause and effect break down. In a model proposed by the theorist David Deutsch in 1991, however, the paradoxes created by CTCs could be avoided at the quantum scale because of the behavior of fundamental particles, which follow only the fuzzy rules of probability rather than strict determinism. “It’s intriguing that you’ve got general relativity predicting these paradoxes, but then you consider them in quantum mechanical terms and the paradoxes go away,” says University of Queensland physicist Tim Ralph. “It makes you wonder whether this is important in terms of formulating a theory that unifies general relativity with quantum mechanics.”

Experimenting with a curve

Recently Ralph and his PhD student Martin Ringbauer led a team that experimentally simulated Deutsch’s model of CTCs for the very first time, testing and confirming many aspects of the two-decades-old theory. Their findings are published in Nature Communications. Much of their simulation revolved around investigating how Deutsch’s model deals with the “grandfather paradox,” a hypothetical scenario in which someone uses a CTC to travel back through time to murder her own grandfather, thus preventing her own later birth. (Scientific American is part of Nature Publishing Group.)

Deutsch’s quantum solution to the grandfather paradox works something like this:

Instead of a human being traversing a CTC to kill her ancestor, imagine that a fundamental particle goes back in time to flip a switch on the particle-generating machine that created it. If the particle flips the switch, the machine emits a particle—the particle—back into the CTC; if the switch isn’t flipped, the machine emits nothing. In this scenario there is no a priori deterministic certainty to the particle’s emission, only a distribution of probabilities. Deutsch’s insight was to postulate self-consistency in the quantum realm, to insist that any particle entering one end of a CTC must emerge at the other end with identical properties. Therefore, a particle emitted by the machine with a probability of one half would enter the CTC and come out the other end to flip the switch with a probability of one half, imbuing itself at birth with a probability of one half of going back to flip the switch. If the particle were a person, she would be born with a one-half probability of killing her grandfather, giving her grandfather a one-half probability of escaping death at her hands—good enough in probabilistic terms to close the causative loop and escape the paradox. Strange though it may be, this solution is in keeping with the known laws of quantum mechanics.

In their new simulation Ralph, Ringbauer and their colleagues studied Deutsch’s model using interactions between pairs of polarized photons within a quantum system that they argue is mathematically equivalent to a single photon traversing a CTC. “We encode their polarization so that the second one acts as kind of a past incarnation of the first,” Ringbauer says. So instead of sending a person through a time loop, they created a stunt double of the person and ran him through a time-loop simulator to see if the doppelganger emerging from a CTC exactly resembled the original person as he was in that moment in the past.

By measuring the polarization states of the second photon after its interaction with the first, across multiple trials the team successfully demonstrated Deutsch’s self-consistency in action. “The state we got at our output, the second photon at the simulated exit of the CTC, was the same as that of our input, the first encoded photon at the CTC entrance,” Ralph says. “Of course, we’re not really sending anything back in time but [the simulation] allows us to study weird evolutions normally not allowed in quantum mechanics.”

Those “weird evolutions” enabled by a CTC, Ringbauer notes, would have remarkable practical applications, such as breaking quantum-based cryptography through the cloning of the quantum states of fundamental particles. “If you can clone quantum states,” he says, “you can violate the Heisenberg uncertainty principle,” which comes in handy in quantum cryptography because the principle forbids simultaneously accurate measurements of certain kinds of paired variables, such as position and momentum. “But if you clone that system, you can measure one quantity in the first and the other quantity in the second, allowing you to decrypt an encoded message.”

“In the presence of CTCs, quantum mechanics allows one to perform very powerful information-processing tasks, much more than we believe classical or even normal quantum computers could do,” says Todd Brun, a physicist at the University of Southern California who was not involved with the team’s experiment. “If the Deutsch model is correct, then this experiment faithfully simulates what could be done with an actual CTC. But this experiment cannot test the Deutsch model itself; that could only be done with access to an actual CTC.”

Alternative reasoning

Deutsch’s model isn’t the only one around, however. In 2009 Seth Lloyd, a theorist at Massachusetts Institute of Technology, proposed an alternative, less radical model of CTCs that resolves the grandfather paradox using quantum teleportation and a technique called post-selection, rather than Deutsch’s quantum self-consistency. With Canadian collaborators, Lloyd went on to perform successful laboratory simulations of his model in 2011. “Deutsch’s theory has a weird effect of destroying correlations,” Lloyd says. “That is, a time traveler who emerges from a Deutschian CTC enters a universe that has nothing to do with the one she exited in the future. By contrast, post-selected CTCs preserve correlations, so that the time traveler returns to the same universe that she remembers in the past.”

This property of Lloyd’s model would make CTCs much less powerful for information processing, although still far superior to what computers could achieve in typical regions of spacetime. “The classes of problems our CTCs could help solve are roughly equivalent to finding needles in haystacks,” Lloyd says. “But a computer in a Deutschian CTC could solve why haystacks exist in the first place.”

Lloyd, though, readily admits the speculative nature of CTCs. “I have no idea which model
is really right. Probably both of them are wrong,” he says. Of course, he adds, the other
possibility is that Hawking is correct, “that CTCs simply don't and cannot exist." Time-travel
party planners should save the champagne for themselves—their hoped-for future guests seem
unlikely to arrive.
161 comments

Stephen Hawking and his caterers are TELLING us no one showed up. If they let is slip that someone from the far future showed up then spilling the beans would create the wrinkle in time that could prevent future events… Just Saying… 😉

My prediction is that some major discoveries relating directly to the notions of causality, determinism, and the feasibility of time travel will be made in the next few decades. There are several avenues of science – not just physics, but also mathematics, theoretical computer science, systems theory, and others – that are all converging on the same fundamental set of problems. It’s going to be fascinating, whatever they discover.

Wow, I really enjoyed reading this article, though I’m not sure I understand what these fellows are really saying. I’m not a mathematician by any stretch and therefore realize my short comings to fully comprehend this

Deutsch’s model of CTCs is saying that the moment a time traveler goes back he creates a divergent reality and it doesn’t matter if the grandfather dies because he’s not YOUR grandfather he is the grandfather of the possible “you” in that new reality. The other guy is saying that if you killed your grandfather suddenly you might not remember anything because you haven’t been born but their exists the possibility of someone preventing you from going back which is how the paradox is avoided.

The problem with quantum mechanics is that it is a statistical approach for measuring reality. So far, it has successfully been used to describe some kinds of physical phenomena more accurately than deterministic theories (mathematical formulas), because those mathematical formulas are based on assumptions that are not entirely accurate. For example, the speed of light through outer space is often assumed to be constant, but it isn’t, because “outer space” is far from being a pure vacuum. Most cubic meters of outer space contain at least a few atoms of hydrogen, many more sub-atomic particles, plus gamma rays and light rays crisscrossing each other from virtually all directions. And when you consider how many cubic meters of outer space a light ray has traveled through (while going from one galaxy to another), it is quite reasonable to assume that outer space itself acts somewhat like a prism (thereby creating a “red tint” which some scientists speculate to be evidence supporting their “big bang theory.”) Also, if all of those galaxies are accelerating away from each other (as “big bang” theorists claim), then how can the Hubble Telescope photograph galaxies that at colliding with each other?

On the other hand, quantum mechanics has been used to support claims that a particle can be “a two different places at the same time”, but that may simply reflect that fact the slice of time used for that experiment was too large to accurately measure where that particle actually was.

So we need to re-examine the fundamental assumptions that are being made in order to create such mathematical models. Is it the speed of light that is constant or is it a precisely measured incremental advancement of time that is really the constant? If the advancement of time (which is part of the “speed of light” formula) is in fact what is really constant, then all this talk about “bending the fabric of space-time) leaves much to be desired.

“On the other hand, quantum mechanics has been used to support claims that a particle can be “a two different places at the same time”, but that may simply reflect that fact the slice of time used for that experiment was too large to accurately measure where that particle actually was.”

The double slit experiment confirmed that particles can be two places at once. The wave/particle duality makes it look that way because when the particle this something (being observed) parts of the wave overlaps and cancels out while other parts of the waves reinforce each other.

Also accurate measuring a particle gets harder not because of time, but because of the amount of energy needed to observe it. At some point, the light waves you use to try and measure both position and velocity will disturb the light wave of the particle and all you’ll come up with is probabilities of where it could be (Heisenberg Principle)

Also, as for the big bang theory and colliding galaxies, I heard it somewhere that the gravitational pull of the two galaxies (in the relatively local sense)exceeds the force of the expansion (Which most physicists will attribute to dark energy vs dark matter) Because the force of the expansion is so weak at greater distances, it doesn’t really affect a galaxies that are relatively close.

There are valid theories about how time travel can be achieved. At the sub atomic particle level time shifting of specific particles have been achieved. This involved very large amounts of power and usage of particle accelerator facilities.

If we look back to the early to mid 1800’s when existence of radio waves may be possible was only a theory by some scientists of the time, there were others commenting that radio waves would be impossible for any human to make. Then when the scientists who were working to make radio waves said these waves may be able to carry intelligent information they were ridiculed and regarded as to being fools.

If we look to the early 1900’s radio broadcast with human voices in real time were being used, and real time pictures (television) was being experimented with.

Before television existed there were engineers and scientists saying this type of medium would be impossible to accomplish. Once accomplished there were engineers saying it would never be practical and reliable to have in the home.

Now we move up a hundred years or so, we can have super high definition television fit in the palm of a person’s hand, where we can see live or recorded pictures instantly from any part of the world.

With television we can look back in to the past because of film, video tape, and now digital recording on a chip that can be made smaller than a human finger nail.

As for time travel, it is interesting that some governments are pouring in a lot of money. This research is being kept very quiet, and is titled under other types of research projects. It is unfortunate that there are people making huge exaggerations about time travel and its existence to make profits from the excitement and fascination with this subject.

Just like everything else that has been accomplished, with all that has been done in various types of science and industry, we have to be opened to all possibilities. Maybe in a few hundred years from now tele-transport and time travel will be common place!

My hypotheses on this subject is, travel to the future it seems would be the impossible journey as for the future has not yet happened. The future does not exist for any one person, only the now and the past.
It would be like trying to climb a set of stairs in a building that has not been built yet.Since the past has happened, then time travel should let one be able to interact with past events.

As to the paradox, well since you are here, you did not kill your grandfather. Most likely you would not be able to do so, as it had not happen in your time line or you would not exist. Doing so may start a divergent time as as others have stated, but that would not effect you.

This is all conjecture though, with out a time machine to test the hypotheses.

Your basic premise may be wrong, and with that your whole argument would fall apart. You assume the future has not happened yet because you view time as linear only. You live it as a line so everything must be that way. You are Cyrano De Bergerac floating to the moon on bottles of morning dew because if there is air down here, then certainly there is air up there.

Uh. We have already proven hay time travel is possible to the future. Any man that has gone into space has actually travel in future on a micro scale. As you get closer to the speed of light, time in fact travels slower for you than other outside the travel

well i think that the fact the we are constantly moving or falling through space as they like to put it then how are you going to send anything back in time say you want to even send me back 15 minutes well 15 minutes ago i was 10k revolutions to the left not to mention how far we have moved in space even a fifteen minute jump might send me 1500 feet into the air just to come crashing down
and to take one body move it through a length of time …. i might end up at the edge of our solar system … do i get a suit for this trip?

Ya know?….people ought to discriminate this topic into catagories of physics and math and metaphysics and then social-science and politics. Fact: So far we haven’t traveled back in time in any way physically. Fact: so far we can do it easily on paper. Fact: if you look at the middle east?…those folks haven’t made it to the year 1900 as yet !!!!!, all we need to do to travel back in time is to go there. Fact: as of the year 2014?….this country has fallen back in time about 35 years to the year 1979, what with our employment crisis and our political crisis’ and our govermentmental woes….I mean geeeeeesh.!!!!! What is goin on man?

I believe that the universe we live in is like a sheet of glass. When you look at it in the front it is a 2d surface but as you turn it you see the 3d perspective. In this dimensional shift if you were to travel back in to time then you would wind up in a parallel universe that may hold another choice you made in your life and the outcome it entails. Thus it is possible to go to another dimension in time on another sheet of glass but not make changes to the existing dimension you came from.

Uh,,,Jerry,..You do keep up with astronomy don’t you?…and you know about all the galaxies that are hundreds of thousdands if not millions of light years away?…..we are observing them in the distant past…..just pointing that out.

If I was an astronaut, I would definitely show up, since, according to special relativity and atomic clocks, they would have traveled to the future even if the shift forward in time was measured in millionths of a second.

Big difference between travel into the future and travel into the past. SH conjectured that travel into the past is effectively impossible, future is possible however would require more energy then our Sun will ever put out to move 1 gram 1/100 of a second into the future.

I’ve long been jealous of persons with job titles such as, “Theorist”. Someone gets paid to think up things that are “statistically possible”. I can and do that all the time for free!

Seriously, though, my belief system is based on science, and rejects religious teachings which require “blind faith”, based on anecdotal “evidence”. Many recent theoretical scientists are putting forth ideas that would have been considered science fiction decades ago. My problem is that “theoretical” literally means conjecture to a certain extent. Granted, conjecture based on mathematical evidence, but conjecture nonetheless. My point being, the line between religion and science, in their explanatory roles concerning the universe has become increasingly blurred – though I remain on the science side of the equation, due to factual evidence being essential to even theoretical ideas.

BTW – “Theo” as a preface means, “relating to God or deities”, so that would suggest a philosophical component to physics.

Theorists do have some pretty important work. They can provide benchmarks for future experiments once we have the tech to do so. They could also lend ideas to problems that aren’t thought about at the moment. They are very intelligent individuals who can think outside the box of physics and not get stuck in tunnel vision. Remember Einstein’s GR and SR were theoretical for a long time until his predictions were actually observed.

Sure some theories turn out to be debunked but I wouldn’t go so far as to say anyone can do it. Even theoretical, it has to be substantiated by a very pedantic community to be accepted.

I wish someone smarter than I could explain this to me. If ya’ll will forgive my arrogance, my reading comp skills are pretty top-notch, and I love science and subjects such as this, but it’s tough for me to actually visualize and comprehend exactly what’s going on and why the grandfather paradox actually get’s resolved. I’m still wondering why there can’t be multiple timelines…. when has that been disproved? Such a thing instantly solves a bunch of time-travel paradox’s. You CAN go back in time and kill your grandfather, because as soon as you go back in time, technically the person being killed is no longer YOUR grandfather. Great, now I feel the need to go smoke a joint……..

for ever change thus creates an alternate reality. like a fork in the road. so if you went into the past then YOUR future would change while everyone from THAT alternate reality would go unchanged. so the idea of changing the past for the sake of mankinds future is irrelevant. It would in essence only change your future. So the whole idea of time travel and changing the past is just selfish. **BUT**…traveling to the future to prevent things from happening for people from your timeline would then benefit because they have yet to experience any of those events. Like a train switching tracks at the last second to avoid a collision.

You do realize this is the year 2014?……even now, talking, even from Hawkings is still dribble on this subject…we haven’t gone to the Moon permanently and we haven’t even gone to Mars yet. We haven’t transported any kind of matter from one place to another using a particle matter beam or even invented a warp drive engine for space travel. It is however somehow just romantic as hell to talk about science fiction as if it was real…Oh Sleep..per chance to dream !!!!! Everybody go to sleep.

If time is infinite, then there will be an infinite number of time travelers and they will visit each second of time an infinite number of times. Don’t try to raise the argument that they may not want to, if time is infinite, atoms (or leptons and quarks if you will) will randomly assemble themselves into an infinite number to time machines with and infinite number of time travelers. Where are they?

If time is not infinite, we need a new theory of time and therefore a new theory of time travel.

as for the grandfather paradox, there is none. IF there was such a thing as a space time continuum, and time travel was a reality, traveling back in time breaks the continuum. The continuum runs throughout a person’s lifetime, and when the life TIME is broken by time travel, there is no longer any connection between the future person and the past person. You could even kill your past self in time travel, and it would not effect the other you.

Agreed!!! Nothing in the universe suddenly “blinks out of existence”, time travel or not. Traveling back in time and killing your grandfather doesn’t suddenly make you fade into nothingness, or spontaneously “wink out” it just turns you into someone who just killed a guy!

You are still thinking of time as a linear thing and not an object like a coordinate in three dimensional space. Nothing prohibits me from taking a piece of paper and folding it such that the piece of paper intersects itself multiple times. Einstein postulated space-time – that is – 4 dimensions. That fourth dimension only appears to be different to us, but in reality, it must act just like the other three dimensions. So, instead of having a piece of paper that represents x,y,z, think of it as representing x,y,t where t is time. When you fold it now, the “t” coordinate can intersect in multiple places so, indeed, there is no lack of continuity.

There was a novel, well-received, written a couple decades ago by physicist Gregory Benford. In his story, the guys doing the experiment think that the one-photon switch just described in the article sort of hangs halfway between off and on, jittering between the two states. It wasn’t clear to me what observer could see it toggling; who possibly exists that can see the switch move?

So pushing it, if there is a 50/50 chance of encountering grandpa, you could basically say that quantum physics will insure that you couldn’t interact with your grandpa at all . No matter how hard you tried , or would send you back. before you could, or create an alternate universe to avoid a paradox. Of course if you could kill grandpa then that would prove the rumors that grandma was unfaithful true.

Maybe no one showed up to his party because they considered him to be a boar and had better ways to spend their time. Maybe time travel won’t be realized until so far in the future that no one knew of it or him. Maybe the human race simply doesn’t survive long enough to realize time travel.

I went to sleep on Tuesday.. Woke up on Wednesday.. But I thought it was still Tuesday all day.. So i went 1 day into the future.. But was temporally existing in the past.. Therefore, I went forward *and* backwards in time in a very small space-time contuum…

If I time traveled to the future, do I not run the risk,(knowing not the inevitable date my death will occur in the future), of arriving at a time after I have deceased, and have I then in fact, short circuited my possible life span, BY TRAVELING BEYOND IT?

No because you’re still you that was propelled into the future. You cant encounter yourself in the future because you haven’t been there yet. That would mean that all time is predetermined. Science fiction likes to play around with encountering a future you from a different timeline that is not yours. If you were able to do that, you would not exist in your timeline until you go back.

It seems to me that if a future time traveler was expected at Dr. Hawkins’ party, he should have sent out invitations to a (anonymous at least) guests through the mail so that such a guest may one day receive it in order to show up at the party. No?

One more sorry. Then devise a means to map the expansion of the universe and our rotations in it, back to a specific point in time? Program that into the crystal too, on to the photon, into the hole, and magically back to 600ad lol

Now I don’t have all the facts mind you, and am going speak crazy but… Wouldn’t it be interesting if they took the experiment, with quantum entanglement and used it with this time travel idea? They spank a qubit of information onto a photon but using this- http://m.inhabitat.com/inhabitat/

The only problems with QE is the Heisenberg Uncertainty Principle. It’s almost impossible to know what state the pairs are in because the more precisely you measure a particle, the more you disturb it. You cant know its position or velocity at any one time. It’s called the EPR paradox or Einstein, Podlosky and Rosen.

Today, using a telescope an astronomer sees stars
being born or dying in events that happened millions
of years ago. I do not know, but it seems what happens
now is happening forever( that’s to the senses of an observer)

We are only seeing the light from the even that occurred millions of years ago. If you could instantly transport to the origin of that light you would view the current state of that object.

As that light travels it also dims since it is being dispersed over a larger and larger sphere so that “event” does not appear as bright here as it did at any distance closer to the originating object.